Stegosaurus Revisionism!!!

Miscellaneous and Personal Stuff I Must Share
41

Well, no one is forcing you to read the thread, are they? Apparently there are some Dopers here who do find this stuff pretty interesting.

As for why it’s interesting I’m assuming you mean all of dinosaur science, and not just the part about the stegosaur plates.) ; from my perspective I wonder how you can not find it interesting that the earth was populated for hundreds of millions of years by bizarre creatures of all shapes and sizes and that we have a completely different ecosystem in place today. How did that happen? What were these animals like? Besides the fact that I just find them to be really neat, there is much that we can potentially learn about life in general from dinosaur science. If we learn something about, for example, their metabolism and can learn more about the overall ecosystem that they lived in, maybe we can learn something about the kinds of changes and growth the earth has gone through over the vast stretches of time. Has the composition of the atmosphere changed since then? What about temperature averages? Can we figure out why we no longer see land animals anywhere near the size of the great sauropods? Moreover, paleontology and specifically dinosaur science has given us some of the best evidence in support of evolution as a fact of history. And certainly since you are posting here, you must have some interest in fighting ignorance, right? Do you oppose learning for learning’s sake?

42

Uh-oh.

43

Seconded.

44

This has been bugging me ever since I read it. From the original article I linked to (bolding mine):

The blood vessels are Dead Ends?!!

Where the hell are there blood vessels that don’t go anywhere? I’ve never heard of such a thing. It’s a circulatory system. If it didn’t circulate, then all the blood would end up at the dead end, and there wouldn’t be anything bringing new oxygen and nutrients to make that area grow. And if the blood is circulating through there, then the argument that the plates can’t be part of a thermoregulatory system disappears.

I suspect that, as often happens, the article got an incomplete or very garbled story that it didn’t understand, and passed on nonetheless. I’ll have to see the real article.
As for all of you who argued that, if such thermoregulatory systems didn’y develop everywhere, and therefore they don’t work, I gotta point out that “Everytrhing not forbidden is compulsory” is not a rule of science or of evolution. I could give you counterexamples. You can find perplxing “sails” or plates on various stegosaurians, as wel as pre-dinosaur types like Dimetrodon and edaphasaur, and on the creature featured in Jurassic Park III, the Spinosaur. I, for one, find it hard cto believe that such elaborate structures evolved as sexual signals.

45

Hey Evolutionary Biologist types - I gotta relevant question (I think/hope/please don’t throw anything at me!!):

  • Okay, stegs had what they had because it advantaged them (gotta love verbifying a noun, right?) evolutionary, given the conditions in which they were living at the time. At some point, conditions changed and they - like all animals - had to evolve to better fit those conditions or die out, right?

  • The two main forces of evolution (he says like he knows what he is talking about) are natural selection and sexual selection.

  • My question: What are the key criteria one uses when deciding if a trait evolved due to natural selection vs. sexual selection? And as a follow up: What are the major implications of deciding a trait is one or the other - if you go one way, what are the key conclusions implied vs. going with the other form of selection?

Thanks!

46

IANAEvolutionaryBiologist, but , in the cases I’ve seen, things that are claimed to be cases of sexual selection are usually blatantly so – something that is present in only one sex, or directly relates to choosing a mate or to the mechinics of mating. This is, of course, a lot more secure for living creatures. When you’re talking about a species we only know from fossils, it’s not even clear what the two sexes even looked like, and suggestions about sexual selection have a big question mark associated with them.
By the way, although adaptive radiation, random mutation, and natural and sexual selection are the means by which evolution occurs, there’s stuill more to it than that. This was, in a way, the thrust of all of Stephen Jay Gould’s essaysd in Natural History – the theme of evolution lurked in the back of all of them, and they’re worth reading. You can’t explain all developments on the basis of a natural selection or sexual selection advantage, for instance. He plays on this theme quite a bit, in one case arguing that the aniomalously large relative size of the kiwi’s egg (IIRC) can be better explained as the result of a remnant of an earlier situation in its lineage, rather than having any advantage.

47

Well why not? Peacocks developed some pretty nutty structures in order to get in good with the ladies. Deer, moose, elk, antelopes, etc all developed horns as species identification—and also to get the ladies. Girl frogs and lizards swoon for boys with big balloons and weird flappy things under their chins. There has even been speculation that the human wiener developed to such a large size (compared to the great apes’) as a visual competition for the ladies. (Yeah, no cite, sorry. I wasn’t about to type “large wiener” into Google at work.)

Compared to the stuff critters do today to differentiate species and get laid, stego plates seem down right mundane.

48

[QUOTE=CalMeacham]
IANAEvolutionaryBiologist, but , in the cases I’ve seen, things that are claimed to be cases of sexual selection are usually blatantly so – something that is present in only one sex, or directly relates to choosing a mate or to the mechinics of mating. This is, of course, a lot more secure for living creatures. When you’re talking about a species we only know from fossils, it’s not even clear what the two sexes even looked like, and suggestions about sexual selection have a big question mark associated with them.
/QUOTE]Isn’t sexual selection merely a subcategory of natural selection? That is, those who are more attractive to the other sex pass on their genes more often than those who are are less attractive. Being attractive is merely a trait just like being bigger and stronger and able to drive all the others away.

49

Nope – feathers were already there, along with muscles to erect them. The tail just got bigger and showier.Ditto for frog pouches and other such things. I can even accept cocks combs as bits of excess skin. But plates and spines are entirely separate and complex structures. Even if used in part for sexual signalling, it seems to me there’d have to be some other function for them to exist in the first place.

I think “natural selection” is used for things that help the individual survive better, whereas “sexual selection” is something that doesn’t necessarily help an individual survive, but makes it more attractive to potential mates, or makes its young more likely to be retained/fertilized/whatever. I’m not sure if that’s the book-correct usage, but it’s what I’ve always understood by it. Big swelling red chests on frigate birds don’t help them survive in the travails of the wild, but they help them pick up chicks.
For thast matter, a big swelling red chest arguably helped attract me to Pepper Mill. But it gets in the way pretty often in the wilds of nature.

50

Yes and no. Yes, in that anything which helps attract mates grants one a higher-than-average chance of subsequently mating, and therefore perpetuating one’s genes. No, in that the product of sexual selection is not adaptation per se (whereas natural selection necessarily leads to adaptation), but typically sexual dimorphism. Sexual selection operates under the principle that it is other members of one’s own species that are doing the selection, rather than the more nebulous “environment”.

The plates likely evolved from the spines, and the spines likely evolved from the already-existing dermal plates that stegosaur ancestors had (Stegosaurs are classified as Thyreophorans - the armored dinosaurs. They had several rows of smaller, bony scutes along the back, neck and tail, similar in arrangement, though not scale, to the armor of their relatives, the ankylosaurs).

51

Ain’t denying that plates evolved from something. Everything starts ftrom something that gives it a toehold. I’m saying that the elaborate structure of the plates (rather than them just being bigger bumps on the back) argues for some other function than simply catching the eye of another stegosaur. Peacock feathers, after all, are just big feathers. Stegosaur plates have a complex and regular geometry far beyond being bigger bumps, or even bigger spines. One of the claims of the thermoregulator bunch was that the up-on-end-diamonfd shape of the plates and their staggered position on the back was just what you’d expect for heat fins.

52

And antlers and horns? Those are pretty complex, where did they come from?

53

Good question, and I confess I don’t know. But I do know that they’re used for butting - and not just other antler-wearers. Antlers and horns aren’t just for impressing the ladies.

Which is another reason I question the suggestion that Triceratops had horns only for ornamentation.

54

One of those Discovery Channel, waiting-for-something-else-to-come-on programs pointed out that the animals grow antlers in breeding season and shed them when they move for the season; they would be really nice to hace to use against predators when moving the herd.

55

IIRC, they keep them well after mating, though. If they were just for mating, they might drop off immediately after. Horns aren’t shed at all. I wouldn’t stand in front of a charging bull, in or out of season.

56

The elaborateness of the plate structure argues for display far more than it does against it - after all, most, if not all, such displays are precisley that: elaborate. You don’t catch the eye of a potential mate by being mundane. As for the actual structure of the plates, studies from 20 years ago showed that there was nothing inherent about the actual plate structure that indicates they would have made good thermoregulators. There was no direct evidence for any advanced circulation system, as would be expected were that their primary function. Indeed, the conclusion reached was that, if anything, the skin on the plates, rather than the plates themselves, might have taken on such a role – but that’s really a no-brainer, as any increased surface area relative to volume is going to function that way. Other, more recent studies (c. 2000) examined the whole of Stegosauria, and found a great deal of variation in plate and spike arrangement, number and design, indicating that the arrangement found in Stegosaurus was neither optimal nor necessary for heat regulation.

Ornithiscians in general evolved numerous forms of ornamentation, from the large, often ornate, headshields of ceratopsians, to the elaborate headdresses of hadrosaurs, to the elaborate spike arrangements of many ankylosaurs. And that’s not even considering the diveristy of ornate headgear that can be found amongst Saurischia, as well.

In other words, within the Dinosauria, we have multiple instances of ornate bumps, hooks and knobs used – most likely – for inter- & intraspecies identification and/or display, offense, and/or defense. We have no verified instances of any structures being used as thermoregulatory devices, or even that such structures would have provided an advantage to their owners (thermoregulating doohickeys being more useful to an ectotherm than to an endotherm; and as I noted before, there are plenty of instances of precursors upon which to build a thermoregulator – especially considering the stego-plates themselves are heavily-derived scutes, which were relatively common throughout Ornithischia – which means other groups would almost certainly have evolved similar structures were they indeed an advantage). As such, why do you consider the thermoregulatory function more logical than the display function?

And yet, we see few, if any, examples of such arrangements in actual heatsinks. Take a look at the wide range of CPU heatsinks, for example. None, to my knowledge, exhibit such a design. See, for example, here, here, here, and here.